Seven members of the Outlaws motorcycle gang were sentenced to life in prison at Birmingham crown court today for the murder of Hells Angel Gerry Tobin.

The men were convicted of killing Tobin on the M40 in August 2007. The two last members of the south Warwickshire chapter of the club on trial were convicted of murder yesterday after jurors deliberated for eight days.

The seven include Sean Creighton, 44, from Coventry, who pleaded guilty to murder and firearms charges before the start of the trial last month.

The 35-year-old mechanic was shot on his way home from a bikers' festival. A green Rover in the outside lane of the M40 pulled alongside him and two shots were fired from different weapons. Tobin was hit just below his helmet and his customised Harley-Davidson spun on for 200 yards before it came to a halt.

Creighton, the man whose finger was on the trigger of one of the guns, claimed to be the "sergeant-at-arms" of the south Warwickshire chapter of the Outlaws, the main rivals to Hells Angels.

Creighton had plans for the Outlaws, long in the shadow of the Angels, to make their mark that weekend. For three days, he and fellow members had been carrying out reconnaissance on the roads round the Bulldog Bash festival in Warwickshire and from 5am that Sunday he had been ordering his fellow members into action.

Police believe the shooting was probably part of the feud between the two gangs and the hit must have been sanctioned at a high level by the Outlaws.

Detective Superintendent Ken Lawrence said: "They are taking a big risk which will have an impact on the whole organisation so it would be illogical to think that a chapter would do that acting alone." He said the chapter could have suggested the hit themselves or could have been given the task by a different part of the organisation. The Bulldog Bash was taking place on their territory.

Creighton directed the operation as the crowd of 30,000 left the festival. Along with two other men, Dane Garside and Turner, he parked the Rover in a layby on the A46 and waited for someone wearing the distinctive Hells Angels death's-head insignia to go past. Three others in the chapter, Dane's brother Karl, Cameron and Taylor, were in a Range Rover further up the motorway.

A seventh member, Bull, was in a third car, apparently acting as a link between the two groups. Creighton had decided that a Hells Angel – any Hells Angel – would die that day.

The Angels had attended the Bulldog Bash for 20 years. In the territorial world of motorcycle clubs, one club entering another's area can be a source of conflict but, according to other bikers, the Angels had long had tacit permission to attend the Bash and would not have had any notion of what awaited one of their members that day.

It is estimated that there are 250 Hells Angels in the UK and slightly fewer Outlaws. The gangs first clashed in the 1960s, when three Angels were murdered in the US.

Because such gangs do not cooperate with the police, detectives thought they were in for a protracted investigation. But while the hit was professional, the planning and the cover-up were amateurish.

The police knew they could be looking for a burnt-out Rover and when one was almost immediately reported, they investigated its pedigree. The name of the registered owner proved to be fictitious but its previous owner was Creighton. The Outlaws had left other clues: Creighton and Dane Garside were seen on CCTV at a nearby petrol station wrapped in hats and warm clothes on a hot summer's day and a search of the chapter's unofficial clubhouse in Coventry yielded two shotguns in a bag with Turner's fingerprints on it.

The detectives also had two unexpected breaks: Bull spoke to them, breaking one of the club's rules, and Creighton, faced with strong evidence against him, decided to plead guilty. Bull was separated from the other defendants in the dock and is in a different prison, now at risk not only from Hells Angels but from other Outlaws. The police speedily arrested all the members of the chapter.

Timothy Raggatt QC, prosecuting, had told the jury of six men and six women: "This wasn't a case of a man being killed for any personal motive or any personal reason. This was a man who was targeted not because of who he was, but because of what he was. In one sense, Gerry Tobin was a random victim."

It emerged yesterday that an Outlaw from a separate chapter has been jailed for 12 years for keeping an "armoury" of weapons in his home. David Melles, 52, was arrested in Cinderford, Gloucestershire, in March, as part of the Tobin investigation. He pleaded guilty to 10 counts of possessing firearms earlier this year.

The sentence could not be reported previously for legal reasons until all verdicts were delivered in the Tobin murder trial.